The purpose of this study is to learn about the risks for human immunodeficiency virus (HIV) and other sexually transmitted infections among gay and bisexual men aged 23-29 years who attend gay-identified public venues. This protocol will be used to (1) estimate the prevalence of HIV infection and markers for hepatitis B, (2) estimate the prevalence of various sexual, drug-use, and needle-sharing behaviors, and to estimate the magnitude of the association of such behaviors with HIV serostatus, (3) estimate the association of 8 psychosocial factors with HIV-related risk behaviors and HIV infection, and (4) characterize the use of medical services and counseling and testing services by members of this population. Studies of established cohorts of gay and bisexual men have documented decreases in both the incidence of HIV infection and the prevalence of high-risk behaviors in these populations. However, data suggest that such reductions may not be occurring among young gay and bisexual men. In Baltimore City between 1990 and 1992, an increasing trend was observed in the seroprevalence of HIV infection among men less than 25 years of age who attended a clinic that primarily serves gay and bisexual men. In a 1992-3 survey of gay and bisexual men aged 17-22 years living in the San Francisco Bay area, the overall prevalence of HIV infection was 9.4%. Among the participants, 33% reported engaging in unprotected anal intercourse in the prior six months and 70% of those who were HIV infected were not aware of this when interviewed. These findings suggest that ongoing community-based HIV/AIDS prevention activities may not be effectively reaching young gay and bisexual men. To address this issue, data are needed on the prevalence of HIV infection and risk behaviors in this population, along with information on risk behaviors, psychosocial factors, and utilization of health and community services.